Light olefins, defined herein as ethylene, propylene, butylene and mixtures thereof, serve as feeds for the production of numerous important chemicals and polymers. Typically, light olefins are produced by cracking petroleum feeds. Because of the limited supply of competitive petroleum feeds, the opportunities to produce low cost light olefins from petroleum feeds are limited. Efforts to develop light olefin production technologies based on alternative feeds have increased.
An important type of alternate feed for the production of light olefins are oxygenates, such as, for example, alcohols, particularly methanol, ethanol, n-propanol, and iso-propanol, dimethyl ether, methyl ethyl ether, diethyl ether, dimethyl carbonate, and methyl formate. Many of these oxygenates may be produced by fermentation, or from synthesis gas derived from natural gas, petroleum liquids, carbonaceous materials, including coal, recycled plastics, municipal wastes, or any organic material. Because of the wide variety of sources, alcohol, alcohol derivatives, and other oxygenates have promise as an economical, non-petroleum source for light olefin production.
Oxygenates can be converted to olefins using various molecular sieve catalysts. This conversion of oxygenates to olefins (OTO) is an exothermic process. Therefore, the reactor outlet temperature is typically higher than the reactor inlet temperature.
Many methods and/or process schemes have been proposed to manage the heat of reaction generated from the exothermic process in order to avoid temperature surges and hot spots. A well managed process can also lead to a reduction of the rate of catalyst deactivation, as well as the production of undesirable products, such as methane, ethane, carbon monoxide and carbonaceous deposits or coke. Such processes tend to involve heating the feed or cooling the effluent to appropriate temperatures and pressures.
U.S. Pat. No. 6,121,504 (Kuechler et al.) discloses a process for catalytically converting a feedstock comprising an oxygenate to olefins. The process includes direct product quenching to increase heat recovery and to improve heat integration. In particular, a heavy product formed in the reaction process is used to provide at least a portion of the heat used to heat the feedstock.
U.S. Patent Application Publication, Pub. No. US 2003/0088136 A1, published May 8, 2003, discloses a process for recovering heat in an oxygenate to olefin production process. The process includes removing heat while maintaining the temperature of an effluent gas stream above the dew point temperature of the effluent gas stream. A step of washing the effluent gas stream to remove solid catalyst particles from the gas stream is also provided.
Well managed utilization of heat in the oxygenate to olefins conversion processes are continuously sought. In addition, well managed processes that result in the reduction of the rate of catalyst deactivation or a reduction in production of undesirable products are also continuously sought.